Automatic irrigation system purging

ABSTRACT

An automated irrigation purge system utilizes a pressure purge method of discharging compressed air from a reservoir through selected irrigation zones with feedback from pressure switches to determine when to open and close each zone valve. No programming or user interaction is required beyond starting the system. The system can operate with a wide variety of irrigation systems, with varying number of zones, pipe lengths, pipe diameters, number and variety of sprinkler heads or outlets, and terrain slope. The system tracks the pressure transition time from high pressure to low pressure for each zone as it is blown out. When the current transition time is within a specified range from the previous transition time, the system knows the water has been sufficiently purged from that zone. The purge system can protect the irrigation system from high-pressure conditions, handle multiple error conditions, and maintain water valve settings during power loss.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to methods and apparatus for automaticallypurging water from irrigation systems.

2. Discussion of Related Art

Irrigation systems installed in regions where cold climate conditionsexist can be damaged by freezing of the water contained in theirrigation system and require winterization to prevent this damage.Compressed air is commonly used to force the water out of the irrigationsystem. Common practice is to hire a contractor who utilizes anindustrial grade, engine driven, air compressor with a high flow ratingat high pressures and a large volume capacity reservoir to connect tothe existing irrigation system. The engine driven air compressor andreservoir are generally large, expensive, and noisy devices pulled by atruck or in the bed of a truck. The contractor must be granted access tothe structure to manually turn off the main water supply. The aircompressor and reservoir are then connected to the existing irrigationsystem outside the structure. The contractor then steps through eachirrigation zone, blowing air through the selected zone forcing the waterout through the sprinkler heads, drips, or misters. The contractorobserves each zone and when only air is being emitted from the sprinklerheads, drips, or misters, they manually move to the next zone.

It is common knowledge to step through the zones one at a time to reducethe amount of air required to purge the water. Also, irrigationcontrollers don't allow more than one zone to be on at a time. Thereforeto open more than one zone valve at a time would require the contractorto find each zone valve box located around the structure and manuallyactuate each zone valve. This is time consuming and many times theremote valve boxes are covered by landscape material and difficult tolocate. By default, most contractors just step through each zone usingthe irrigation controller.

It is well known that a home owner can achieve similar purge resultswith a smaller air compressor and reservoir but take significantlylonger to run and may require multiple cycles per zone. Both methods arelabor intensive and require the operator to work outside inuncomfortable, cold climate conditions. Both the contractor andhomeowner have to be diligent in observing air pressures so as to notdamage the irrigation system by exceeding the rating of the piping, thevalves, or the sprinkler heads.

Depending on weather conditions and the time of year, the irrigationsystem user must estimate when they want the system purged of water. Ifthey err on the conservative side and purge the system too soon, theymay have landscape damage if warm, dry weather returns. If they err onthe aggressive side and purge the system too late, they may haveirrigation system freeze damage. Once purged, they are hesitant to turnthe water back on due to the inability to have it purged again that sameday and the expense involved.

New landscaping and existing trees and shrubs require watering in colddry months. It becomes cumbersome and time consuming to pull out thegarden hose and water the landscaping during cold weather. Thelandscaping can be easily watered using the irrigation system thenimmediately followed by an automatic purge of the system.

Bailey in U.S. Pat. App. No. 2011/0079654, teaches a purging system thatis mainly flow based over a given amount of time. It utilizes anexpensive, complicated air supply pump and feedback system where itmaintains a consistent pressure in the zone by adjusting the speed ofthe air supply. Variable speed motors require expensive controllers.Also, in order to monitor the pressure in the system, a more expensivepressure sensor must be used to provide continuous pressure feedback.Even with only one zone open at a time, the flow based systems requirelarge capacity flow pumps, with a very high cubic-feet per minutecapability, to reach a stable pressure once the water has been forcedfrom the zone. The flow rate of air that can be emitted from a sprinklerhead is greater than the flow rate of water that can be emitted.Therefore, to reach a stable air pressure, large flow rates must bemaintained and seem overkill for the simple task being accomplished.Also, Bailey has stated that the necessary outputs of the air source mayincrease if there is no air reservoir to assist with the purging.

Irrigation systems are designed to operate with water pressures up to 80psi. The purge system that quickly discharges compressed air from an airreservoir, known as the pressure purge method, staying below pressuresof 80 psi, has proven to be the most economical and accommodative to thewidest range of irrigation piping systems and air compressors. Asuccessful irrigation purge system should accommodate unique irrigationsystems with varying number of zones, unequal pipe lengths, differentpipe diameters, different number and variety of sprinkler heads oroutlets, and varying degrees of slope of the terrain being irrigated.Also, users who already own a suitable air compressor will prefer to useit in conjunction with the purge system.

There is a need in the art for methods and apparatus for automaticallypurging water from irrigation systems such as an irrigation purge systemthat can utilize a common, traditional air compressor on unique anddiverse irrigation piping in a cost effective manner, protect the systemfrom high pressure conditions, be fully automatic, know when each zonehas been purged of water, handle multiple error conditions, maintainwater valve settings without consuming power and during a power loss orunplugged condition, and seamlessly integrate with all irrigationcontrollers.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide methods andapparatus for automatically purging water from irrigation systems.

An improved fully automated irrigation purge system according to thepresent invention utilizes a pressure purge method of dischargingcompressed air from a reservoir through selected irrigation zones withfeedback from pressure switches to determine when to open and close eachirrigation zone valve. No programming or user interaction is requiredbeyond starting the system. The system can be used with any commercialirrigation controller. It can be successfully utilized in a wide varietyof irrigation systems, with different number of zones, various pipelengths, different pipe diameters, different number and variety ofsprinkler heads or outlets, and varying degrees of slope of the terrainbeing irrigated. The air reservoir can be charged at any reasonable rateusing a traditional 120 VAC air compressor. A higher airflow ratecompressor will take less time to charge the reservoir than a lowerairflow rate compressor, but both will accomplish the task. The aircompressor and reservoir can be disconnected and used elsewhere when notneeded for purging.

Advantages of this improved irrigation purge system include providing asimplified, cost effective means of automatically purging the irrigationsystem of water. The improved purge system can be added to an existingirrigation system or can be installed with a new irrigation system. Itsmounting is flexible and can be placed in the structure next to theirrigation controller or next to the irrigation water supply, whereverthere is a 120 VAC outlet. It can be implemented with an automaticlatching water valve or with a manual water valve. The purge systemautomatically tracks the pressure transition time from high pressure tolow pressure for each zone. For example, a drop in pressure from 60 psito 10 psi could constitute a pressure transition. When the currentpressure transition time is within a specified range from the previouspressure transition time, the system knows the water has beensufficiently purged from that zone. Still further advantages will becomeapparent from a study of the following description and the accompanyingdrawings.

As a feature, the automatic purge system of the present invention canprotect the irrigation system from high pressure conditions, be fullyautomatic, know when each zone has been sufficiently purged of water,handle multiple error conditions, maintain water valve settings during apower loss or unplugged condition, and seamlessly integrate withcommercial irrigation controllers.

A method of automatically purging an irrigation system according to thepresent invention includes the steps of removing water pressure to thesystem, designating an irrigation zone to blow-out, blowing water out ofthe designated zone using pressurized air, tracking pressure within theirrigation system from a high pressure to a low pressure state, whereinthe designated zone is blown-out when the low pressure state is reached,designating a new irrigation zone, and repeating these steps until alldesired zones are blown-out, and blowing out the desired zones aspecified number of times or cycles.

In some embodiments the specified number of blow-out cycles for eachzone is determined by the steps of measuring the amount of time for adesignated zone to be blown-out, comparing the measured blow-out time toa reference time, and setting the specified number of blow-out cyclesfor the designated zone to a number based on comparing the measuredblow-out time to the reference blow-out time.

For example, the invention might compare the measured blow-out time toeither a predetermined time or to a previously measured blow-out timeand set the specified number of blow-out cycles to the current number ofblow-out cycles when the measured blow-out time is within a desiredmargin of either a predetermined time or of a previously measuredblow-out time. In general, the specified number of blow-out cycles iseither set to a predetermined value or is set to a value based on aprevious amount of time for a zone to be blown-out.

In some embodiments each irrigation zone is blown-out in sequence andthe process is repeated until the specified number of blow-out cycles isreached. As a feature, a designated zone is skipped in the sequence oncea specified number of blow-out cycles is reached for that specifiedzone.

In other embodiments, each designated zone is blown-out until thespecified number of blow-out cycles is reached for that designated zoneand then a new zone is designated.

Apparatus for automatically purging an irrigation system according tothe invention includes an irrigation controller (either existing orintegrated) controlling water flow into a plurality of irrigation zones,a low-pressure switch for determining when pressure within theirrigation system passes a low-pressure threshold, a high-pressureswitch for determining when pressure within the irrigation system passesa high-pressure threshold, a source of compressed air; and a purgecontroller including circuitry constructed and arranged to determinepressure within the irrigation system by monitoring the low-pressureswitch and the high-pressure switch; and to apply compressed air todesignated irrigation zones to blow water out of the designatedirrigation zones based upon the pressure within the irrigation system.

The purge controller might further include circuitry for defining adesignated zone as blown-out when the pressure within the irrigationsystem goes from a high pressure state to a low pressure state, andcircuitry for blowing out each designated zone until a specified numberof blow-out cycles is reached. Further, it may include circuitry formeasuring the amount of time a designated zone takes to be blown-out andfor setting the specified number of blow-out cycles based upon ameasured blow-out time.

Generally the circuitry for setting the specified number of blow-outcycles further includes circuitry for limiting the specified number ofblow-out cycles to a maximum value. The purge controller may include aswitch, such as a three-way switch connected to the purge controller,the switch and the purge controller constructed and arranged such thatthe purge controller allows water to flow to the irrigation system,prevents water from flowing to the irrigation system, or purges theirrigation system according to the position of the switch.Alternatively, two two-way switches may be used.

The invention may include a latching solenoid controlled by the purgecontroller for selectively allowing water to flow to the irrigationsystem. It may also include a quick-release connection for compressedair so that a homeowner may attach a portable air compressor. In someembodiments a control panel is provided and includes the switch and LEDsto notify the homeowner of the state of the system. Preferably, thepurge controller uses the irrigation controller's power source(conventionally 24 VAC) to drive the irrigation zone valves. The purgecontroller's power source may be independent of the irrigationcontroller and they would be optically isolated from each other. Thisarrangement would protect the control circuitry of the irrigationcontroller.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (Prior Art) is a physical block diagram which illustrates anexisting irrigation system.

FIG. 2A is a physical block diagram illustrating an automatic purgingapparatus according to the present invention used in conjunction with atypical irrigation system such as that shown in FIG. 1. FIG. 2B is anexample of a control station for use with the purging apparatus.

FIG. 3 includes FIGS. 3A and 3B comprising time flow diagramsillustrating a method of automatically purging an irrigation systemaccording to the present invention.

FIG. 4 is an electrical block diagram illustrating control andinformation flow between automatic purging apparatus according to thepresent invention and a typical irrigation system.

FIG. 5 comprises FIGS. 5A-5G and shows an example circuit diagram ofautomatic purging apparatus according to the present invention.

FIG. 6 comprises FIGS. 6A-60 and shows detailed flow diagramsillustrating a specific embodiment of the present invention in detail.

FIG. 7 comprises FIGS. 7A-7G, comprising plots illustrating experimentaldata gathered with apparatus and methods according to the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The following table lists elements of the illustrated embodiments of theinvention and their associated reference numbers for convenience.

TABLE 1 REFERENCE NUMERALS 10 purge system 11 latching solenoid watervalve 12 low-pressure switch 13 check valve 14 high-pressure switch 15air reservoir 16 air compressor 17 Purge Controller 18 optional manualwater valve 19 manual water valve with drain port 20 tee, insidestructure air injection point 21 quick disconnect 22 quick disconnect 23back flow check valve 24 outside structure air injection point 25irrigation controller 26 irrigation zone valve(s) 27 sprinkler heads,drips, and misters 28 water supply 29 tee 30 to facility's plumbing 31green LED 32 red LED 33 purge controller selector switch 40 zone valvecontrol cables 41 air compressor indicator panel 42 pressure switchesindicator panel 43 zone purging indicator panel 44 latching solenoidwater valve indicator panel

FIG. 1 (Prior Art) is a physical block diagram illustrating an existingirrigation system. Water supply 28 supplies the facility's plumbing 30and the irrigation system. A manual water valve with drain point 19permits a user to manually shut off water to the irrigation system. Airinjection point 24 allows the irrigation system to be blown out withcompressed air. Backflow check valve 23 prevents water from flowingbackward from the irrigation system. Irrigation controller 25 controlswhich irrigation zone valve 26 is open (generally only one valve at atime). If Irrigation Controller 25 opens a zone valve and water pressureis present, that zone is irrigated by sprinkler heads, drips, misters,etc. 27.

The irrigation system is purged as follows. Water valve 19 is closed toshut off water to the irrigation system. If the human operator purgingthe system has access to the Irrigation Controller 25, Controller 25opens and closes the zone valves as the operator directs. Otherwise, theoperator must physically open and close the zone valves 26 to the zones.In either case, the zone valve to the first zone is opened and air isinjected at injection point 24, blowing out residue water in the firstzone. Then the first valve is closed and the zone valve to the secondzone is opened and the second zone is blown-out and so on. After all ofthe zones are blown-out, the operator must go back and repeat the wholeprocess, as only a portion of the water in each zone can be blown out ineach cycle. The process may be repeated three or more cycles in order toensure that the water remaining in the zones is minimal enough not tocause damage to the system if it freezes. The operator then drains thewater from the back flow check valve 23 to inside the structure at themanual water valve drain port 19 to ensure excessive water is notpresent in the pipe exposed to the freezing temperatures outside thestructure.

FIG. 2A is a physical block diagram illustrating an automatic purgingapparatus 10 used in conjunction with the irrigation system of FIG. 1.Purge System 10 includes Purge Controller 17, an air compressor 16 andair reservoir 15, a high-pressure switch 14, a low-pressure switch 12,an internal air injection point 20, and various valves and connections11, 13, 18, 21, 22. Purge Controller 17 takes over the functionsperformed by Irrigation Controller 25, controlling zone valves 26leading to watering elements 27.

In a preferred embodiment, Purge Controller 17 requires no interactionfrom the operator beyond starting the purge process. Hence, in thisembodiment, Purge Controller 17 closes solenoid water valve 11 beforestarting the purge, and the operator is not required to manually closevalve 19.

Latching solenoid water valve 11 is placed in the water supply line tothe irrigation system downstream of manual water valve with drain port19 and upstream of air injection point 20. Another smaller optionalmanual water valve 18 may be placed in line for serviceability oflow-pressure switch 12 and check valve 13. A high-pressure switch 14 islocated downstream and on the air side of check valve 13. Furtherdownstream is air reservoir 15 and air compressor 16. Both can be quickcoupled to the system using quick disconnects 21 and 22. This allows theair compressor 16 and air reservoir 15 to be used for other applicationswhen not needed to purge the irrigation system.

Main water supply line 28 feeds to the facility or structure 30 and isdirected to the irrigation system by tee 29. Back flow check valve 23and traditional air injection point 24 are located outside the structureat the highest point in the irrigation system. Multiple irrigation zonevalves 26 are located downstream of the back flow check valve 23 andthey control when water flows to the multitude of sprinkler heads,drips, or misters 27 in each zone. When the system is not being purged,Irrigation Controller 25 controls the opening and closing of irrigationzone valves 26 by switching 24 VAC to the solenoid located at each zonevalve 26. Purge Controller 17 can perform this same function, forexample by using the same 24 VAC power source used by IrrigationController 25 and closing a relay within Purge Controller 17 to providepower to the selected irrigation zone valve 26.

FIG. 2B illustrates a control station that might be used in conjunctionwith purge system 10. While it is not necessary for a user to monitorthe operation of Purge Controller 17 in detail, such a control stationmay be desirable for some users. Purge Controller 17 includes a selectorswitch 33, which may be set to “Water Off,” “Water on,” or “Purge.” Aset of LEDs (generally a green “OK” LED 31 and a red “Error” LED 32) areused to notify the user of the state of the system. Table 2 belowindicates a set of errors and associated LED blink signals. Zoneindicator lights 43, an air compressor indicator 41, pressure switchindicators 42, and a latching water solenoid valve indicator 44 areoptional. Conventional irrigation system controller 25 might be locatedon the control station panel for convenience.

When Purge Controller 17 is set to “Water On” via selector switch 33,Purge Controller 17 checks for error conditions, turns on the water, andcontinues to monitor the position of selector switch 33 as well as thepositions of low-pressure switch 12 and high-pressure switch 14. Fromthere, the irrigation system runs in the traditional manner. Irrigationcontroller 25 provides control signals to zone valves 26 as shown inFIG. 1.

FIGS. 6C and 6D show the process Purge Controller 17 follows in detailwhen “Water On” is selected. One important action Purge Controller 17takes is to cycle the water valve on and off several times in shortintervals. This action slowly fills the irrigation system with waterwhich in turn prevents water hammer from damaging valves, pipes, andpipe fittings.

When Purge Controller 17 is set to “Water Off,” Purge Controller 17turns off the air compressor 16, latching solenoid water valve 11, andall irrigation zone valves 26. FIGS. 6A and 6B show the process PurgeController 17 follows in detail when “Water Off” is selected. Forexample, Purge Controller 17 will check the water pressure vialow-pressure switch 12 to ensure that the water pressure drops afterlatching solenoid water valve 11 is closed and an irrigation zone valve26 is opened, and provide an error signal if this doesn't occur.

When selector 33 is set to “Purge,” Purge Controller 17 can controlirrigation zone valves 26. In general, irrigation controller 25 canstill control irrigation valves 26 as well, although it may be desirableto lock-out irrigation controller 25 in some embodiments. FIGS. 3A and3B show the purge process at a high level and FIGS. 6E-H show it indetail.

FIGS. 3A and 3B are high level time flow diagrams illustrating a methodof automatically purging an irrigation system according to the presentinvention. FIG. 3A illustrates the overall method. The operator startsthe purge process, for example by turning purge controller selector 33from either “Water On” or “Water Off” to “Purge” (step 102). PurgeController 17 turns off the water supply (step 104) by closing latchingsolenoid water valve 11. As an alternative, the operator may shut offthe water manually using manual water valve with drain port 19 beforeselecting “Purge”.

Next, the system allows water to flow out of a zone and verifies thatthe water is turned off. Purge Controller 17 opens a zone valve 26 (step106) to allow water to flow out and existing water pressure to drop.Purge Controller 17 monitors low-pressure switch 12 to ensure that thewater pressure drops sufficiently to ensure that the water supply isindeed turned off (step 108). Purge Controller 17 then closes the openzone valve (step 110).

The system blows out a zone several times, or cycles. When a zone issufficiently cleared of water, it is considered purged. The systemensures that a zone is purged by comparing the amount of time it took toblow-out a zone to a Pressure Transition Time Value. Before the purgeprocess starts, Purge Controller 17 sets the Pressure Transition TimeValue to a selected reference time (step 112). As an example, thestarting Pressure Transition Time Value (for the first blow-out cycle)might be set to 0 to indicate this is the first blow-out cycle and nocomparison can take place. As an alternative, the starting PressureTransition Time Value might be set to a reference time such as 10seconds. This is the Pressure Transition Time Value used in the firstblow-out cycle through the zones. After that, the last pressuretransition time for each zone is used to calculate the new PressureTransition Time Value for that zone (step 114, detailed in FIG. 3B).When all the zones have been purged (step 116) the process is completedin step 118 by turning off air compressor 16, releasing remainingcompressed air in the air reservoir 15, and verifying that the pressureremains below the low-pressure switch 12 threshold, showing that airpressure to the system has been eliminated. The process ends at 120.

FIG. 3B is a flow diagram detailing the processes performed in step 114.For the selected zone, Purge Controller 17 turns on air compressor 16(step 202) and monitors the high-pressure switch 14. When thehigh-pressure switch threshold is reached, Purge Controller 17 allowspressure to build up for a few more seconds and then turns off the aircompressor 16 (step 206) and is then ready to blow-out a zone.

Purge Controller 17 opens irrigation zone valve 26 for the selected zone(step 208) and monitors first the high-pressure switch 14 (step 210) andthen the low-pressure switch 12 (step 210) to determine when thepressure has dropped sufficiently. At that point, the zone valve isclosed (step 212) and the blow-out time is noted. If the blow-out timeis either below a designated minimum time or within a defined margin ofthe Comparison Time, the zone is marked as sufficiently purged and isskipped during the next blow-out cycle.

As a feature, the system may provide error notifications to the system(and the user if desired) when events do not proceed as planned. Forexample, in step 210, if the low-pressure switch 12 threshold is notreached within a certain amount of time after the zone vale is opened,an error code can be provided indicating that something is wrong withthe zone (e.g. a pipe is blocked, or the zone does not exist). Table 2,below indicates examples of codes that may be provided by the system tothe user, using red LED 32. FIGS. 6A-H show how these error codes areassigned and how they might be used to monitor the state of theirrigation system in more detail.

TABLE 2 Number of Blinks (red LED 32) Error detected 1 Latching SolenoidWater Valve 11 is on but low-pressure switch 12 stays low detecting thelack of water pressure (indicates a defective latching solenoid watervalve, a defective low-pressure switch 12, a leak, or water turned offat some other point). 2 Latching Solenoid Water Valve 11 is on andlow-pressure switch 12 is on but high-pressure switch is on detectingpresence of high air pressure and the air pressure is not needed(indicates air reservoir 15 was connected with pressure already presentor defective high-pressure switch 14). 3 Latching Solenoid Water Valve11 is off but low-pressure switch is high detecting the presence ofwater pressure (indicates Latching Solenoid Water Valve 11 is defective,inoperable, manually turned on, or a leak into the system or defectivelow-pressure switch 12). 4 Latching Solenoid Water Valve 11 is off andlow-pressure switch is low, but high-pressure switch 14 is on, detectingthe presence of air pressure that is not needed (indicates the airreservoir was connected with pressure already present or defectivehigh-pressure switch 14). 5 System attempted to purge but air pressuredidn't build fast enough, low-pressure switch is on but high-pressureswitch is off and did not close in time (indicates a problem with aircompressor 16 or an air leak or defective high-pressure switch 14). 6Not assigned 7 Attempted to purge but air pressure remains low and didnot build fast enough, low-pressure switch 12 is off and high-pressureswitch 14 is off (indicates that air is leaking in the zone, anirrigation zone valve 16 failed to close, irrigation controller 25 hasopened an irrigation zone valve 26, or the back flow check valve 23dropped open). 8 Attempted to purge but air pressure does not drop quickenough, high-pressure switch 14 is off and low-pressure switch 12 is onand did not transition in time (indicates a clog or restriction in thezone, an irrigation zone valve 26 closed unexpectedly that allowedenough air to escape to turn off high-pressure switch 14 but not enoughair to escape to turn off low-pressure switch 12, or defectivelow-pressure switch 12). 9 Not assigned 10 Not assigned 11 Internal use

The error detection capability of some embodiments may be used forpurposes beyond detecting a problem during normal operation. A user maydo system testing deliberately. For example, a user may detect a leak inthe irrigation hardware by turning the purge controller selector switch33 to “Water On”, waiting for the water pressure to rise and achieving asolid green OK LED, then turning the water off manually using ManualWater Valve 19 and determining how long it takes for water pressure tosubside again when the red error code 1 appears. The faster the drop inpressure the larger the leak.

FIG. 4 is an electrical block diagram illustrating control andinformation flow between automatic purging apparatus according to thepresent invention and a typical irrigation system. Purge controller 17includes selector switch 33. It controls air compressor 16, LEDs 31 and32, and latching solenoid water valve 11. It shares control ofirrigation zone valves 26 as described previously. It monitorslow-pressure switch 12 and high-pressure switch 14. Irrigationcontroller 25 could be one of many commercially available irrigationsystems. In the embodiment of FIG. 4, irrigation controller 25 provides24 VAC power to Purge Controller 17. In alternative embodiments,irrigation controller 25 could be integrated within Purge Controller 17,or Purge Controller 17 and irrigation controller 25 could be integratedtogether, eliminating the need to provide separate 120 VAC power to eachcontroller and to connect the controllers with an external cable 40.

FIG. 5 comprises FIGS. 5A-5G and shows an example circuit diagram ofautomatic purging apparatus according to the present invention.

FIG. 6 comprises FIGS. 6A-60 and shows detailed flow diagramsillustrating a specific embodiment of the present invention in detail.FIGS. 6A-6C illustrate the process performed when purge controllerselector switch 33 is turned to “Water Off,” or if it remains in “WaterOff” after power was removed from Purge Controller 17. FIG. 6Dillustrates the housekeeping process performed when purge controllerselector switch 33 was in the “Water Off” position and continues to bein the “Water Off” position (no change). FIGS. 6E-6G illustrate theprocess performed when purge controller selector switch 33 is turned to“Water On.” FIGS. 6H-60 illustrate the process performed when purgecontroller selector switch 33 is turned to “Purge.” The processesperformed by the embodiment of FIG. 6 produce the error codes shown inTable 2, and this embodiment was used to generate the data shown inTable 3 and FIG. 7.

FIG. 7 comprises FIGS. 7A-7G, comprising plots illustrating experimentaldata gathered with apparatus and methods according to the presentinvention, and in particular the embodiment of FIG. 6. Table 3 belowprovides data associated with the plots.

TABLE 3 Purge Data Date: 6 May 2012 Time Purge Start: 3:01:00 PM TimePurge End: 4:11:30 PM Reservoir: 5 Gallon Compressor: 3.7 SCFM at 40 PSI2.6 SCFM at 90 PSI Code: TIME_BOARD_01CC.HEX Pressure Transition Timefor Each Zone, Each Cycle in seconds Cycle Number Zone 1 2 3 4 5 1 46.5716.77 14.14 11.55 10.37 2 25.25 16.45 14.45 12.13 12.02 3 32.11 16.1613.16 11.52 4 11.84 8.41 7.81 5 65.65 45.84 41.63 6 16.02 10.23 9.008.51 7 18.78 14.29 14.14 Time Difference Between Cycles in Percent Zone1-2 Diff 2-3 Diff 3-4 Diff 4-5 Diff 1 −178% −19% −22% −11% 2  −53% −14%−19%  −1% 3  −99% −23% −14% skip 4  −41%  −8% skip skip 5  −43% −10%skip skip 6  −57% −14%  −6% skip 7  −31%  −1% skip skip

While the exemplary preferred embodiments of the present invention aredescribed herein with particularity, those skilled in the art willappreciate various changes, additions, and applications other than thosespecifically mentioned, which are within the spirit of this invention.What is claimed is:

1. Apparatus for automatically purging an irrigation system having anirrigation controller controlling water flow and air flow into aplurality of irrigation zones, the apparatus comprising: a low-pressureswitch for determining when pressure within the irrigation system passesa low-pressure threshold; a high-pressure switch for determining whenpressure within the irrigation system passes a high-pressure threshold;a timer configured to measure pressure transition times based on theamount of time between a high pressure threshold and a low pressurethreshold; a source of compressed air; and a purge controller includingcircuitry constructed and arranged to monitor the low-pressure switchand the high-pressure switch, to designate irrigation zones, and toapply compressed air to designated irrigation zones to blow water out ofthe designated irrigation zones based upon the low-pressure switch andthe high-pressure switch; wherein the purge controller is furtherconstructed and arranged to automatically blow out designated zones aspecified number of blow-out cycles, wherein the number of blow-outcycles is specified based on a measured pressure transition time andwherein an irrigation zone is purged after it is blown-out the specifiednumber of cycles.
 2. The apparatus of claim 1 wherein the purgecontroller further comprises circuitry for measuring an initial pressuretransition time a designated zone takes to be blown-out and for settingthe specified number of blow-out cycles based upon the initial pressuretransition time.
 3. The apparatus of claim 1 wherein the purgecontroller further comprises circuitry for measuring a current pressuretransition time a designated zone takes to be blown-out and for settingthe specified number of blow-out cycles based upon the current pressuretransition time.
 4. The apparatus of claim 3 wherein the circuitry forsetting the specified number of blow-out cycles further includescircuitry for limiting the specified number of blow-out cycles to amaximum value.
 5. The apparatus of claim 1 further comprising a switchconnected to the purge controller, the switch and the purge controllerconstructed and arranged such that the purge controller allows water toflow to the irrigation system, prevents water from flowing to theirrigation system, or purges the irrigation system according to theposition of the switch.
 6. The apparatus of claim 1 further comprising alatching solenoid valve controlled by the purge controller forselectively allowing water to flow to the irrigation system.
 7. Theapparatus of claim 1 wherein the source of compressed air comprises aquick-release connection for connecting to an air compressor and whereinthe purge controller selectively turns on the air compressor.
 8. Theapparatus of claim 1 further comprising a monitoring station controlledby the purge controller including an LED display for indicating thestate of the system.
 9. The apparatus of claim 8 wherein the displayincludes lights configured to indicate a system error.
 10. The apparatusof claim 9 wherein the display includes lights configured to indicatezones being purged.
 11. The apparatus of claim 8 further comprising: aswitch configured to allow a user to selectively activate the purgecontroller.
 12. The apparatus of claim 11 wherein the switch is furtherconfigured to selectively allow water to flow to the irrigation system.13. The apparatus of claim 1 wherein the purge controller and theirrigation controller share a common power source for poweringirrigation zone valves which is optically isolated from the purgecontroller's internal power supply.
 14. The apparatus of claim 1,further comprising a valve configured to prevent water flow back into awater source.
 15. The apparatus of claim 1, further comprising a valveconfigured to prevent water flow back into the source of compressed air.16. The apparatus of claim 15, wherein the valve comprises a check valvedisposed between the low-pressure switch and the high-pressure switch.17. The apparatus of claim 1, further comprising circuitry configured tostore a current state of the apparatus and to restore the state of theapparatus after a power failure.
 18. The apparatus of claim 1, furthercomprising a 120 VAC switch configured to selectively activate thesource of compressed air according to the purge controller.